OF THE STRUCTURE OF WOOD AND HERBS. 95 



them taper to a point, but some of them, as is seen, are rounded and 

 knobbed at the end. The narrow boundary extending from A to 13, indicates 

 the position of the skin of the bark, and within the bark itself the vessels are va- 

 riously arranged. In the band just below A B they are small, much crowded to- 

 gether, and very compact ; while those next in order towards the centre are 

 larger. Next succeeds a row of vessels in arched clusters, extending from H to I, 

 the cells being exceedingly small and crowded together by hundreds in one arch. 

 Below these a ring of large tubes are seen stretching ovel*from K to L. This 

 latter class are termed milk-vessels, on account of their containing a milky liquid 

 peculiar to the Sumach. The wood below D C is filled with pores, which seem 

 to be disposed without regard to any particular order ; but the radial divisions 

 of cellular tissue evidently tend towards a regular arrangement. A waving 

 band of sap-vessels extends from E to F, bordering the edge of the wood where 

 the pith commences. 



WORMWOOD. In drawing 144 is presented a magnified representation of an 

 eighth part of a transverse section of a stalk of Wormwood. It is a structure of 

 extreme regularity, and the great size of the pith, compared with that of the wood, 

 shows at a glance its herbaceous character. The bark includes the whole of 

 the surface A B C D, the wood occupying only the space D C E F, while the 

 pith comprises all the rest of the figure as lar as G. The spherical cavities of the 

 cellular tissue form a broad ring extending in thickness from A to H, and within 

 this space a number of large vessels, as the one at b, are situated ; arranged in a 

 circular row along the inner margin of the ring of cellular tissue. These are 

 termed the resiniferous or gum-vessels, which secrete the aromatic fluid peculiar 

 to the plant. Some vessels of this kind are also found within the pith, two of 

 which are delineated just above E X F. The semi-circular figures e d f, &c., are 

 clusters of sap-vessels, and span the sections in a row from K to I. Within the 

 woody part the spiral vessels are seen, but quite thinly and irregularly scattered. 

 The broad insertions in the woody part, and which diverge from each other as 

 if proceeding from the centre, are the rays of cellular tissue, which in this plant 

 are seen to be of comparatively great thickness, and commence and terminate 

 in a different manner from the same rays in wood. For here, instead of being 

 distinct lines, they are beheld arched at both extremities and united with each 

 other. Moreover they do not terminate where the wood ends, on the line D C, 

 but extend nearly half their length into the bark, enclosing the semi-circular 

 clusters of sap-vessels. The pith, as is evident, is very porous, consisting of a 

 vast number of large cells. 



ROOT OF WORMWOOD. The structure of the roots of plants is similar to that 

 of the trunk, being formed of the same textures disposed in a corresponding 

 manner. Sections of roots display a symmetry and elegance of arrangement by 

 no means inferior to that revealed in transverse slices of wood. In drawing 145 

 is delineated a cross section of the root of Wormwood of its natural size, and in 



